Дисертації з теми "Ionospheric modeling"
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Arora, Balwinder Singh Amrit Singh. "Ionospheric modeling for low frequency radioastronomy." Thesis, Curtin University, 2016. http://hdl.handle.net/20.500.11937/56529.
Повний текст джерелаMoraes, Alison de Oliveira. "Advances in statistical modeling of ionospheric scintillation." Instituto Tecnológico de Aeronáutica, 2013. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=2240.
Повний текст джерелаIsmail, Atikah. "Fourier spectral methods for numerical modeling of ionospheric processes." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-03142009-040454/.
Повний текст джерелаBrosie, Kayla Nicole. "Ionospheric Scintillation Prediction, Modeling, and Observation Techniques for the August 2017 Solar Eclipse." Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/78710.
Повний текст джерелаMaster of Science
Deshpande, Kshitija Bharat. "Investigation of High Latitude Ionospheric Irregularities utilizing Modeling and GPS Observations." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/49507.
Повний текст джерелаPh. D.
Lyu, Haixia. "Contributions to ionospheric modeling with GNSS in mapping function, tomography and polar electron." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/670334.
Повний текст джерелаelectrones en resolución vertical baja y alta a partir de medidas GNSS terrestres y a bordo de satélites de órbita baja (LEO), además de utilizar medidas GNSS desde buques y medidas DORIS, además de mejorar el conocimiento de la climatología de la ionosfera en las regiones polares y en latitudes medias del hemisferio norte. Las contribuciones se pueden resumir en los siguientes cuatro aspectos: La primera contribución consiste en proponer un nuevo concepto de función de mapeo ionosférico: la función de mapeo ionosférico de Barcelona (BIMF), con el fin de mejorar la precisión de conversión de STEC (contenido total de electrones inclinado) a partir de cualquier modelo de VTEC (contenido total de electrones vertical). BIMF se basa en el modelado climático de la fracción VTEC en la segunda capa - μ2, que es el subproducto de UQRG generado por UPC. La primera implementación de BIMF es BIMF-nml para las latitudes medias del hemisferio norte. μ2 se modela en función del dia y la hora local. Desde la perspectiva del usuario, BIMF es la combinación lineal de μ2 y la función de mapeo ionosférico estándar, y solo necesita 41 coeficientes constantes, lo que hace que BIMF sea facilmente aplicable. Su buen comportamiento se demostró en la evaluación dSTEC para diferentes IGS GIM: UQRG, CODG y JPLG. La segunda contribución se centró en confirmar la capacidad de los GIM UQRG para detectar características ionosféricas representativas en regiones polares a través de seis estudios de casos, que incluyen lenguas de ionización (TOI), depresión de ionización en forma de canal, sucesos de transferencia de flujo, theta-aurora, patrones de convección ionosférica y densidad aumentada durante tormentas geomagnéticas. Los datos a largo plazo de VTEC y μ2 proporcionan valiosas bases de datos para estudiar la morfología y climatología de los fenómenos ionosféricos polares. Los resultados de agrupamiento no supervisados de la distribución normalizada de VTEC muestran que los TOI y los parches en los casquetes polares exhiben una dependencia anual, es decir, la mayoría de los TOI y parches ocurren en el invierno del Hemisferio Norte y el verano del Hemisferio Sur. La tercera contribución ha consistido en proponer un método híbrido: AVHIRO (el modelo híbrido Abel-VaryChap a partir de datos de RO incompletos en la parte superior), para resolver un problema de rango deficiente en la recuperación de la densidad electrónica con el modelo de Abel. Este trabajo está motivado por el futuro sistema polar EUMETSAT de segunda generación, que proporciona datos truncados de RO ionosférica, sólo por debajo de las alturas de impacto de 500 km, con el fin de garantizar una recopilación completa de medidas de la parte neutra. AVHIRO aprovecha un modelo Linear Vary-Chap, donde la altura de la escala aumenta linealmente con la altitud por encima del pico de la capa F2, y utiliza la búsqueda Powell para resolver las densidades completas de electrones, el término de ambig ¨ uedad y cuatro parámetros del modelo Vary-Chap simultáneamente, teniendo en cuenta las interacciones no lineales entre los parámetros desconocidos. La cuarta contribución es aprovechar la geometría aportada por la combinación de datos GPS DORIS, Galileo en tierra, LEO-POD y en barco, e incorporar las mediciones de la fase de la portadora de doble frecuencia de múltiples fuentes en el modelo tomográfico para mejorar la precisión de estimación de GIM VTEC. El impacto de agregar cada tipo de mediciones, que son datos de Galileo, datos de GPS basados en embarcaciones, datos de GPS DORIS y LEO-POD, a datos de GPS terrestres en productos GIM se examina de acuerdo con dos criterios de evaluación complementarios, comparación con VTEC[JASON-3] y con dSTEC[GPS]. Este estudio demuestra el mejor rendimiento esperado de GIM por la nueva ingesta de datos en el modelo tomográfico, que es un exitoso paso adelante desde la concepción hasta la validación experimental inicial.
Aghakarimi, Armin. "Local Modeling Of The Ionospheric Vertical Total Electron Content (vtec) Using Particle Filter." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614867/index.pdf.
Повний текст джерелаR2011 software has been used for programing all processes and algorithms of the study.
Kindervatter, Tim. "Survey of Ionospheric Propagation Effects and Modeling Techniques for Mitigation of GPS Error." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1515106508878179.
Повний текст джерелаPinkepank, James Alan. "The applicability of neural networks to ionospheric modeling in support of relocatable over-the-horizon radar." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA286114.
Повний текст джерелаEltrass, Ahmed Said Hassan Ahmed. "The Mid-Latitude Ionosphere: Modeling and Analysis of Plasma Wave Irregularities and the Potential Impact on GPS Signals." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/51804.
Повний текст джерелаPh. D.
Perna, Luigi <1985>. "Ionospheric Plasma Response to the Anomalous Minimum of the Solar Cycle 23/24: Modeling and Comparison with IRI-2012." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/7861/1/Perna_Luigi_tesi.pdf.
Повний текст джерелаChakraborty, Shibaji. "Characterization and Modeling of Solar Flare Effects in the Ionosphere Observed by HF Instruments." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103706.
Повний текст джерелаDoctor of Philosophy
The Earth's ionosphere, extending from about 60 km to 1000 km in altitude, is an electrically charged region of the upper atmosphere that exists primarily due to ionization by solar X-ray and extreme ultraviolet radiation. The ionosphere is an effective barrier to energetic electromagnetic (EM) radiation and charged particles originating from the Sun or any other extraterrestrial sources and protect us against harmful space radiation. High frequency (HF, 3-30 MHz) radio communication, broadly used for real-time medium and long-range communication, is strongly dependent on the state of the ionosphere, which is susceptible to solar activities, such as solar flares, solar energetic particles (SEPs), and coronal mass ejections (CMEs). Specifically, we are interested in the impacts of solar flares. In this study, we use Super Dual Auroral Radar Network (SuperDARN) HF radars, ground-based riometers, and coordinated spacecraft observations to investigate the driving mechanisms of various space weather impacts on the ionosphere and radiowave propagation following solar flares. We begin in Chapter 2 with a characterization of various kinds of ionospheric disturbances manifested in SuperDARN backscattered signal following solar flares. Specifically, we characterized HF absorption effects and frequency anomalies experienced by traveling radiowaves, also known as Shortwave Fadeout (SWF) and Sudden Frequency Deviations (SFDs), respectively. In SuperDARN HF radar observations, SFDs are recorded as a sudden enhancement in Doppler velocity, which is referred to as the ``Doppler flash''. In Chapter 3, we investigate a special event study that elucidates the nonlinear physics behind HF absorption caused by multiple simultaneous solar flares and flares co-occurring with SEPs and CMEs. In Chapter 4, we explore an inertial property of the ionosphere, known as sluggishness, and its dependence on solar flares can provide important information about the chemical proprieties of the ionosphere. We found that the enhanced solar radiation during a solar flare increases the molecular vibrational and rotational energy that in turn enhances the electron detachment rate and reduces ionospheric sluggishness. In Chapter 5, we describe a framework to estimate HF absorption observed by riometers following solar flares. We analyze the influence of different physical parameters, such as collision frequency and electron temperature, on HF absorption. In Chapter 6, we delved into the physical processes that drive the Doppler flash in SuperDARN observations following solar flares. We find, (i) the Doppler flash is predominately driven by change in the F-region refractive index and (ii) a combination of solar flare-driven enhancement in photoionization, and change in zonal electric field and(or) ionospheric conductivity reduces upward ion-drift, which produces a lowering effect in the F-region HF radiowave reflection height. Taken together, these research findings provide new insights into solar flare impacts on the ionosphere and could be used to improve forecasting of ionospheric space weather disturbances following solar flares.
Fu, Haiyang. "Modeling of Plasma Irregularities Associated with Artificially Created Dusty Plasmas in the Near-Earth Space Environment." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19248.
Повний текст джерелаPh. D.
Da, Dalt Federico. "Ionospheric modelling and data assimilation." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665450.
Повний текст джерелаSibanda, Patrick. "Challenges in topside ionospheric modelling over South Africa." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005238.
Повний текст джерелаEdwards, Thomas Raymond. "Empirical Ionospheric Models: The Road To Conductivity." Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/100284.
Повний текст джерелаDoctor of Philosophy
Akel, Junior Alberto Fares. "Modelagem de propagação subionosférica de ondas de frequência muito baixa." Universidade Presbiteriana Mackenzie, 2015. http://tede.mackenzie.br/jspui/handle/tede/1529.
Повний текст джерелаFundação de Amparo a Pesquisa do Estado de São Paulo
We study the behavior of the Earth-ionosphere waveguide through the modeling of the propagation of very low frequency radio waves (VLF). We use the computational model LWPC (Long Wave Propagation Capability) to estimate changes in amplitude and phase of the VLF signals detected by the SAVNET network (South America VLF NETwork), and thus try to understand the behavior of the lower ionosphere under different ionization conditions. The research was divided into two parts. The first part investigates the behavior of the VLF signals in quiescent regimes of ionization. Amplitude and phase simulations for the were carried out, modifying adapting polynomials for the β and h parameters (or Wait s parameters) as a function of the zenithal angle. The second part of this research, uses these polynomials in the study of the lower ionosphere under transient ionization regimes in two distinct conditions: first during of solar flares and second during solar eclipse. For the simulations under solar flare conditions, we calculate the changes in β and ℎ′ parameters during the 25/03/2008 solar explosion. With these values, we calculate the electronic density profile through an exponential model and we find that the electronic density at 75 km is ∼ 104 cm−3, that is twenty times higher than during quiescent conditions. To evaluate our parameter estimates, we calculate the variation of the Wait s parameters for the case of twelve solar events of different classes. We note that the variations Δℎ′ found in this work are larger than that in Muraoka, Murata e Sato (1977) because they consider the variations in the conductivity gradient. For the solar eclipse simulations on 11/07/2011, we investigate its effect on the VLF phase. For this, we use the obscuration coefficient to estimate the guide height variation along the whole path during the eclipse. The simulations reproduce the phase behavior during the eclipse. However, a delay of about twenty four minutes was observed between the simulated and observed measurements. The observed delay is a direct consequence of own estimates of the perturbed ionospheric height and it causal relation with the obscuration during the eclipse. lower ionosphere, VLF, modeling, ionospheric disturbances, solar flares, solar eclipse.
Neste trabalho realizamos o estudo do comportamento do guia de ondas terra-ionosfera através da modelagem da propagação ondas de rádio de frequência muito baixa (VLF). Para isto, utilizamos o modelo computacional LWPC (Long Wave Propagation Capability) para estimar as variações de amplitude e fase de sinais de VLF detectados nos trajetos da rede SAVNET (South America VLF NETwork) e assim compreender o comportamento da baixa ionosfera em diferentes regimes de ionização. A pesquisa foi dividida em duas partes. A primeira parte, investigou o comportamento do sinal VLF em regimes quiescente de ionização, assim realizou-se simulações de amplitude e fase adaptando polinômios que definem os parâmetros β e ℎ′ (ou parâmetros de Wait) em função do ângulo zenital solar. Na segunda parte desta pesquisa, aplicou-se os polinômios no estudo da baixa ionosfera sob regimes transientes de ionização em duas condições distintas. A primeira para o caso de explosões solares e a segunda um para eclipse solar. Nas simulações relativas a explosões solares, calculamos as variações dos parâmetros β e ℎ′ durante o evento do dia 25/03/2008. Com esses valores, calculamos o perfil de densidade eletrônica, através de um modelo exponencial e observamos que a densidade eletrônica em 75 km é ∼ 104 cm−3, ou seja, vinte vezes maiores que antes da explosão. Para avaliar nossas estimativas, calculamos a variação dos parâmetros de Wait para doze eventos de diferentes classes. Observamos que as variações Δℎ′ neste trabalho são sempre maiores do que as descritas em Muraoka, Murata e Sato (1977), devido elas considerarem as variações no gradiente de condutividade. Nas simulações relativa ao eclipse solar do dia 11/07/2011, investigamos seu efeito na fase observada. Para esse estudo, utilizou-se o coeficiente de obscurecimento para realizar as simulações, desta forma foi possível estimar a variação da altura do guia ao longo de todo o trajeto durante o eclipse. As simulações reproduziram o comportamento da fase durante o eclipse. Entretanto, foi observado um atraso entre as medidas calculadas e observadas de aproximadamente ∼ vinte e quatro minutos. O atraso observado é diretamente decorrente da estimativa da altura de referência da ionosfera pertubada e de sua relação causal com o obscurecimento durante o eclipse.
Bryers, Carl. "Quantitative modelling of ionospheric modification experiments at EISCAT." Thesis, Lancaster University, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.675678.
Повний текст джерелаBlanch, Llosa Estefania. "Comportamiento característico de la estructura vertical de la ionosfera en condiciones de calma y perturbadas." Doctoral thesis, Universitat Ramon Llull, 2009. http://hdl.handle.net/10803/9320.
Повний текст джерелаEsta investigación se ha centrado en profundizar en el conocimiento del comportamiento de la estructura vertical de la región F de la ionosfera, tanto en condiciones de calma como perturbadas, y en su modelado mediante funciones analíticas. Las pretensiones de esta investigación han estado motivadas por las discrepancias existentes entre las predicciones ionosféricas del espesor y la forma del perfil de densidad de la región F en condiciones de calma y su variación característica, y por la ausencia de un modelo capaz de reproducir la respuesta de la altura del máximo de ionización a condiciones perturbadas. En esta investigación se ha determinado el comportamiento patrón del espesor y la forma del perfil de densidad electrónica de la región F en condiciones de calma (determinados por los parámetros B0 y B1 del modelo Internacional de Referencia de la Ionosfera, IRI) en un amplio rango de longitudes y latitudes. Con esto, se ha desarrollado un modelo global para cada parámetro mediante una formulación analítica simple que simula las variaciones temporales de éstos en condiciones de calma. La simulación de estos modelos mejora (en términos del error cuadrático medio, RMSE) las predicciones del IRI en un 40% para B0 y en un 20% para B1. También se ha caracterizado la reacción de la altura del máximo de ionización, hmF2, en latitudes medias y condiciones magnéticamente perturbadas, y se ha determinado un comportamiento sistemático de dicha perturbación, ∆hmF2, cuya morfología depende del campo magnético interplanetario (IMF), del tiempo local, de la estación del año y de la latitud. Con ello, se ha desarrollado un modelo empírico que simula la perturbación en hmF2 resultante durante tormentas geomagnéticas intensas mediante funciones analíticas. Este modelo predice los eventos de ∆hmF2 con un 86% de acierto sin generar falsas alarmas y con un RMSE de 40 km respecto a los valores experimentales, que es equivalente al rango de variación experimental obtenido en condiciones de calma. Finalmente, resaltar que también han sido objeto de estudio en esta investigación los mecanismos responsables del comportamiento ionosférico tanto en condiciones de calma como perturbadas y, especialmente, el modelo de tormenta basado en el papel rector de la circulación del viento neutro termosférico.
The main objective of this research is to improve the knowledge on the vertical structure of the ionospheric F region during both, quiet and disturbed conditions, and its modelling by analytical functions. The main motivations of this research were the existing discrepancies between the predictions of the F region electron density profile thickness and shape during quiet conditions and their characteristic variation, and the absence of a model capable to reproduce the electron density peak height response to disturbed conditions. In this research, the pattern behaviour for quiet conditions of the F region electron density profile thickness and shape (determined by the International Reference Ionosphere model (IRI) parameters B0 and B1) was determined in a wide range of longitudes and latitudes. Then, a global model was developed for each parameter using a simple analytical formulation that simulates their temporal variations during quiet conditions. These model simulations improve (in terms of the root mean square error, RMSE) the IRI predictions by 40 % for B0 and by 20 % for B1. The reaction of the electron density peak height, hmF2, at mid latitudes and magnetically disturbed conditions, was also characterized and the systematic behaviour of this disturbance, ∆hmF2, was determined. The morphology of this disturbance depends on the interplanetary magnetic field (IMF), local time, season and latitude. Furthermore, an empirical model was developed to simulate the hmF2 disturbance during intense geomagnetic storms using analytical functions. This model predicts the ∆hmF2 events with a success of 86 % without generating false alarms and with a RMSE of 40 km with respect to the experimental values, which is equivalent to the experimental variation range obtained during quiet conditions. Finally, the mechanisms responsible of the ionospheric behaviour during both, quiet and disturbed conditions, were also studied in this research, specially the storm model based on the leading role of the thermospheric neutral wind circulation.
Petrie, Elizabeth Jane. "Modelling higher-order ionospheric effects on global GPS solutions." Thesis, University of Newcastle Upon Tyne, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612620.
Повний текст джерелаDubazane, Makhosonke Berthwell. "Modelling Ionospheric vertical drifts over the African low latitude region." Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/63356.
Повний текст джерелаAbdullah, Mardina. "Modelling and determination of ionospheric effects on relative GPS measurements." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410711.
Повний текст джерелаWeigel, Robert Scott. "Prediction and modeling of magnetospheric substorms /." Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004399.
Повний текст джерелаWohlwend, Christian Stephen. "Modeling the Electrodynamics of the Low-Latitude Ionosphere." DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/11.
Повний текст джерелаKero, A. (Antti). "Ionospheric D-region studies by means of active heating experiments and modelling." Doctoral thesis, University of Oulu, 2008. http://urn.fi/urn:isbn:9789514289163.
Повний текст джерелаUwamahoro, Jean Claude. "Single station TEC modelling during storm conditions." Thesis, Rhodes University, 2016. http://hdl.handle.net/10962/d1020325.
Повний текст джерелаNohutcu, Metin. "Development Of A Matlab Based Software Package For Ionosphere Modeling." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611229/index.pdf.
Повний текст джерелаbased ionosphere modeling software, i.e. TECmapper is developed within the study. The software uses three different algorithms for the modeling of the Vertical Total Electron Content (VTEC) of the ionosphere, namely, 2D B-spline, 3D B-spline and spherical harmonic models. The study includes modifications for the original forms of the B-spline and the spherical harmonic approaches. In order to decrease the effect of outliers in the data a robust regression algorithm is utilized as an alternative to the least squares estimation. Besides, two regularization methods are employed to stabilize the ill-conditioned problems in parameter estimation stage. The software and models are tested on a real data set from ground-based GPS receivers over Turkey. Results indicate that the B-spline models are more successful for the local or regional modeling of the VTEC. However, spherical harmonics should be preferred for global applications since the B-spline approach is based on Euclidean theory.
Skone, Susan. "Wide area ionosphere grid modelling in the auroral region." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0030/NQ38507.pdf.
Повний текст джерелаEnnis, Alison Elisabeth. "Mathematcal modelling of vibrationally excited nitrogen in the ionosphere." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389732.
Повний текст джерелаGrandin, M. (Maxime). "Multi-instrument and modelling studies of the ionospheres at Earth and Mars." Doctoral thesis, University of Oulu, 2018. http://urn.fi/urn:isbn:9789526216157.
Повний текст джерелаTiivistelmä Tämä väitöskirja tutkii Maapallon ja Marsin ionosfäärejä yhdistämällä useiden eri instrumenttien havaintoja, joilla saadaan tietoa planeettojen ympäristöistä. Maapallon ionosfääriä koskeva työ tutkii aurinkotuuli–magnetosfääri–ionosfäärikytkentää, kun taas Marsin ionosfääriä koskevan työn tavoite on uuden radio-okkultaatiomittauksen data-analyysimenetelmän kehittäminen, joka tuottaa ilmakehän ja ionosfäärin profiileja. Maan ionosfäärin tapauksessa yhdessä julkaisussa tutkitaan nopeiden aurinkotuulivirtausten vaikutuksia F-kerroksen elektronitiheyteen ja toisessa julkaisussa tutkitaan energeettisten (>30 keV) elektronien sateesta johtuvaa kosmisen radiokohinan absorptiota D-kerroksessa. Ensimmäisessä julkaisussa on kehitetty uusi versio data-analyysimenetelmästä, jota kutsutaan vaihelukituksi epookkien superpositiomenetelmäksi. Julkaisun päätulos on, että nopeiden aurinkotuulivirtausten aikana F-kerroksen maksimielektronitiheys pienenee iltapäivän ja illan sektoreilla. Tämä voidaan selittää johtuvan siitä, että ioni-neutraalitörmäysten synnyttämä kitkalämpö kasvattaa ionilämpötilaa ja aiheuttaa lisäksi ilmakehän laajenemisen. Molemmat prosessit kasvattavat elektronien häviönopeutta. F-kerroksen elektronitiheysmaksimi puolestaan kasvaa sektorilla, joka ulottuu keskiyöstä aamun kautta keskipäivään, ja tämä johtuu matalaenergeettisestä elektronisateesta. Toisessa julkaisussa havaitaan, että lisääntynyt kosmisen radiokohinan absorptio kestää jopa neljä päivää nopean aurinkotuulivirtauksen saavuttua Maan kohdalle. Tämä johtuu siitä, että alimyrskyitse injektoidut energeettiset elektronit satavat keskiyön ja aamun ionosfääriin, pääasiassa revontuliovaalin alueella. Kolmas julkaisu raportoi ensimmäistä kertaa havainnon sykkiviin revontuliin liittyvästä kosmisen radiokohinan absorptiosta n. 10 s jaksollisuudella. Tämä osoittaa, että elektronivuon energeettinen komponentti on moduloitu samalla jaksollisuudella kuin revontulielektronien energiat (1–10 keV). Marsissa on tehty radio-okkultaatiomittauksia vuodesta 2004 saakka Mars Express -luotaimen avulla. Vaitoskirjassa on kehitetty uusi datan analyysimenetelmä, joka perustuu numeeriseen simulointiin radioaaltojen etenemisestä Marsin ilmakehässä ja ionosfäärissä. Tämän lähestymistavan avulla vältetään tähän asti käytetyn klassisen inversiomenetelmän rajoitukset. Lisäksi menetelmä tuottaa uusia parametrejä kuten ionitiheysprofiileja. Uutta menetelmää testattiin tulkiten kahden radio-okkultaatiomittauksen aineistoa
Résumé Le travail présenté dans ce manuscrit de thèse s'articule autour de l'étude des ionosphères terrestre et martienne. Une approche multi-instrumentale est adoptée afin de combiner des observations permettant de mettre en perspective des manifestations de phénomènes physiques de natures différentes mais intervenant dans un même contexte global. Le travail doctoral comporte également un volet modélisation. Le manuscrit de thèse consiste en une partie introductrice à laquelle sont adossées cinq publications dans des revues scientifiques à comité de lecture. La partie introductrice de ce manuscrit de thèse a pour objectif de présenter le contexte scientifique sur lequel est basé le travail doctoral. Un premier chapitre passe en revue les principaux aspects théoriques dans lesquels s'inscrivent les études dont les résultats sont publiés dans les cinq articles. Les atmosphères et ionosphères de la Terre et de Mars y sont succinctement décrites, de même que les interactions entre ces planètes et le vent solaire, comprenant notamment la formation de magnétosphères. Les deux chapitres suivants présentent les instruments dont sont issues les données utilisées dans ce travail doctoral ainsi que les méthodes d'analyse des données. Le quatrième chapitre résume les principaux résultats obtenus autour des trois grandes thématiques abordées au cours de cette thèse. Enfin, des pistes quant à la continuation potentielle du travail présenté dans ce manuscrit de thèse sont évoquées en conclusion. Le premier article porte sur une étude statistique des effets des courants de vent solaire rapide sur la région F de l'ionosphère aurorale. Il s'appuie sur des données mesurées par l'ionosonde de Sodankylä entre 2006 et 2008. Au cours de cette période, 95 événements associés à des courants de vent solaire rapide ont été sélectionnés, et la réponse de l'ionosphère au-dessus de Sodankylä a été étudiée à partir des fréquences critiques des régions E et F de l'ionosphère, qui donnent la valeur du pic de concentration électronique dans ces deux régions. Pour cela, une version modifiée de la méthode des époques superposées a été développée, appelée “méthode des époques superposées avec verrouillage de phase”. Une augmentation du pic de concentration des régions E et F est observée du côté nuit et le matin, en lien avec une activité aurorale accrue, tandis qu'une déplétion de la région F est révélée aux temps magnétiques locaux situés entre 12 h et 23 h. Une estimation des effets d'une possible modification de l'équilibre photo-chimique résultant d'un accroissement du chauffage issu de la friction entre les ions et les éléments neutres est proposée. Le deuxième article s'intéresse aux précipitations énergétiques dans l'ionosphère aurorale durant ces mêmes 95 événements, en étudiant l'absorption du bruit cosmique qui en résulte. Il apparaît que les événements au cours desquels le vent solaire demeure rapide pendant plusieurs jours produisent davantage de précipitations énergétiques, qui peuvent atteindre les latitudes subaurorales. Par ailleurs, trois types de précipitations énergétiques sont étudiés séparément, selon qu'elles sont associées avec des signatures de sous-orage magnétique, avec des pulsations géomagnétiques, ou ni l'un ni l'autre. Les deux premiers types de précipitations semblent liés. En effet, l'analyse des données suggère que les électrons énergétiques sont injectés dans la magnétosphère interne durant les sous-orages. Tandis qu'une partie d'entre eux précipitent immédiatement du côté nuit, d'autres dérivent vers le côté matin, où ils subissent des interactions avec des ondes électromagnétiques de type siffleur (whistler en anglais), qui peuvent être modulées par des pulsations géomagnétiques, menant à leur précipitation. Le troisième article présente pour la première fois l'observation de signatures d'aurore pulsante dans des données d'absorption du bruit cosmique. Ces signatures sont consistantes avec les pulsations observables dans l'émission aurorale, et semblent indiquer une modulation cohérente des composantes aurorale (1–10 keV) et énergétique (> 30 keV) du spectre des précipitations électroniques au cours d'une aurore pulsante. Le quatrième article introduit une nouvelle méthode proposée pour analyser les données de radio-occultation mesurées par la sonde Mars Express. Cette approche vise à contourner des difficultés posées par les hypothèses fortes nécessaires à la mise en œuvre de la méthode classique d'inversion, notamment celle d'un environnement martien à symétrie sphérique — qui n'est pas acceptable lors de sondages proches du terminateur jour-nuit. La nouvelle méthode est basée sur la modélisation de l'atmosphère et de l'ionosphère de Mars, et sur la simulation de la propagation des ondes radio entre la station sol sur Terre et Mars Express lors d'une expérience de radio-occultation. Les paramètres libres contrôlant les profils atmosphériques et ionosphériques sont ajustés afin que la simulation reproduise le plus fidèlement possible les mesures. Le cinquième article est une réponse à un commentaire sur l'article précédent. Il vise d'une part à répondre aux critiques émises sur la méthode développée, montrant que celles-ci n'en remettent en cause ni la validité ni la pertinence, et d'autre part à y apporter quelques améliorations
Hong, Chang-Ki. "Efficient differential code bias and ionosphere modeling and their impact on the network-based GPS positioning." Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1190083730.
Повний текст джерелаWyllie, Scott John, and scott wyllie@rmit edu au. "Modelling the Temporal Variation of the Ionosphere in a Network-RTK Environment." RMIT University. Mathematical and Geospatial Sciences, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080617.161323.
Повний текст джерелаShao, Yixie. "World-wide analysis and modelling of the ionospheric and plasmaspheric electron contents by means of radio occultations." Doctoral thesis, Universitat Politècnica de Catalunya, 2019. http://hdl.handle.net/10803/665985.
Повний текст джерелаLa recerca feta en aquesta dissertació consisteix en l'estudi de la ionosfera mitjançant tècniques d'Ocultació Ràdio (RO) de GPS. La primera part s'enfoca en la metodologia d'extracció de perfils de les mesures RO. L'objectiu és l'obtenció de perfils més precisos mesurats a partir de les dades. La inversió clàssica d'Abel és una metodologia emprada àmpliament en l'obtenció de RO, tant mateix l'error introduït per l'assumpció de simetria també és reconegut. En ordre d'eliminar aquest error en estudis previs el Separability Method (SM) va ser desenvolupat. En el present treball es revisa i es valida la millora en el mètode clàssic aportada per SM. SM té un millor comportament inclús quan s'exclou l'error de Lack of Collocation (CoL). La precisió dels resultats depenen també de l'exactitud del GIM's suportats (p.ex. Com més exacte són els GIM's emprats millor són els resultats obtinguts). L'error de SM introduït pel modelatge incorrecte en utilitzar el Vertical Total Electron Content (VTEC) en lloc del ECLEO (el contingut d'electrons per sota de l'altura LEO) també és revisat. Els resultats mostren que només tenen un impacte mínim en les mesures extretes de RO. La segona part és un estudi de la climatologia de la part superior de la ionosfera I la part inferior de la plasmaesfera basat en l'extracció RO mitjançant SM amb l'objectiu de donar una imatge general de les característiques I tres d'aquestes dues regions en diferents períodes solars; el mínim solar de 2007 i el màxim solar de 2014. Dos models empírics bi-component, el model STIP i el model CPD, utilitzats per separar la contribució de la ionosfera i la plasmaesfera al VTEC, s?han estudiat i validat. Addicionalment també es discuteix sobre les condicions de l'aplicació de STIP. També es fa el mateix amb altres models empírics. Es mostra la imatge de la part superior de la ionosfera fins a un límit definit d'altitud el qual és determinat per l'altitud de satèl·lit Low Earth Orbit (LEO) que s?ha utilitzat per observar les RO. S'utilitza el model per derivar les transicions d'altitud hu I l'escala d'altitud hs durant aquests dos anys. Generalment, hu i hs mostren clarament dependències cícliques diürnals, estacionals i solars. És introduït i estudiat el concepte d'IONf, la fracció de contribució de la ionosfera al VTEC. Es mostren els atributs ionosfèrics i la majoria d'anomalies ionosfèriques es veuen plasmaesfera a través d'aquest mesura. En comparació amb altres paràmetres ionosfèrics, com ara Ecion i Ecpl, el contingut d'electrons de la ionosfera i la plasmaesfera IONf, és més estable. Degut això és més idoni pel modelatge de la ionosfera. El Model del Capacitador és emprat per modelar congruentment el procés de càrrega ionosfèrica' durant el sector de l'alba fins al migdia, mostrant que el model representa de manera bastant fidedigna les dades reals en diferents circumstàncies i durant els periodes de màxima i mínima activitat solar
Hartkorn, Oliver [Verfasser], Joachim [Gutachter] Saur, and Bülent [Gutachter] Tezkan. "Modeling Callisto's Ionosphere, Airglow and Magnetic Field Environment / Oliver Hartkorn ; Gutachter: Joachim Saur, Bülent Tezkan." Köln : Universitäts- und Stadtbibliothek Köln, 2017. http://d-nb.info/1138359459/34.
Повний текст джерелаQahwash, Murad M. "High frequency communication system modeling and performance enhancement, employing novel adaptive DSP techniques." Doctoral diss., University of Central Florida, 2002. http://digital.library.ucf.edu/cdm/ref/collection/RTD/id/1383.
Повний текст джерелаHigh Frequency (HF) communication has been shown to be a useful communication technique from the very beginning of World War I and it accelerated during World War 11. This is attributed to its simplicity, ability to provide near globe connectivity at low power without repeaters, moderate cost, and ease of proliferation [I]. In fact, the HF communication system utilizes the ionosphere [2][3][4] to refract the skywave signals to a distant receiver. This ionospheric channel has some disadvantages. First, it is a non-stationary channel as the HF frequency propagation is a function of the sun spot activities, solar winds, and diurnal variations of the ionization level [5]. Second, the channel produces distortion in both signal amplitude and phase. As the different ionospheric layers move up or down, independent Doppler shifts on each propagation mode are introduced. Multipath fading [6] caused by multiple refractions of the signal fiom the ionosphere with or without ground reflection causes performance degradation in the HF system. Some techniques have been developed to improve HF performance [I]. One example is Space-Diversity [7], which uses more than one antenna at distant spaces to combine the received signal. Angle-of-Arrival Diversity that takes advantage of the fact that different modes have different arrival angles at the receiver, and so, highly directional antenna for example, can be used to improve the system performance. Another method of improving HF performance is to use different frequencies to transmit and receive messages. This method is known as Frequency diversity. Using timediversity, one can add a degree of redundancy to the transmitted message through the use of different types of coding, interleaving, etc. In the military standard, MIL-STD- 1 88- 1 1 OA [8], a convolutional encoder [9][10] followed by interleaver [Ill-[14] was used to scramble and transmit the data in different bit rates. In the presence of multipath fading [ 1 51, a training sequence is transmitted in an interleaved fashion with the data symbols with a 50% duty cycle. This has the disadvantage of losing half the bandwidth. At present, the recent advances of the Digital Signal Processing (DSP) [16][17] make it possible to reduce the bit-error-rate BEY and increase the transmission bit rate [18] through the usage of adaptive equalization [ 191-[2 11 which will be the focus of this dissertation. Equalizers such as, Transversal Equalizer [ 1 61, Blind Equalizer [22], Training waveform Equalizer [23], and Minimum Mean Square Error (MMSE) [20] Adaptive Equalizer have been applied into various communication systems. This proposal work will be to initially apply some of the previous developed equalizer to the HF channel specifically. Thereafter, new adaptive channel equalization [24],[25] will be developed to compensate for transmission channel impairments due to bandwidth limitations, multipath propagation, and rayleigh fading [2 11 conditions in mobile environments. A new technique for frequency offset prediction has been developed and finally, a new approach for MIL-STD- 1 88- 1 1 0A high frequency single-tone modem employing orthogonal Walsh-PN codes has been implemented.
Ph.D.
Doctorate;
Department of Electrical and Computer Engineering
Engineering and Computer Science
Electrical Engineering and Computer Science
198 p.
xviii, 198 leaves, bound : ill., (some col.) ; 28 cm.
Mannix, Christopher Robert. "Measuring and modelling the impact of the ionosphere on space based synthetic aperture radars." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6869/.
Повний текст джерелаChiaretta, Marco. "Numerical modelling of Langmuir probe measurements for the Swarm spacecraft." Thesis, Uppsala universitet, Rymd- och plasmafysik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-148633.
Повний текст джерелаZou, Li. "A modelling study of HF radar coherent detection of irregularities in the high-latitude ionosphere." Thesis, University of Leicester, 1997. http://hdl.handle.net/2381/30604.
Повний текст джерелаChen, Chin-Hung. "Modeling and Observational Studies of Plasma Density Anomalies and Earthquake-triggered Disturbances in the Mid-latitude Ionosphere." 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/157786.
Повний текст джерелаHabarulema, John Bosco. "A contribution to TEC modelling over Southern Africa using GPS data." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1005241.
Повний текст джерелаLimberger, Marco [Verfasser], Urs [Akademischer Betreuer] Hugentobler, Michael [Akademischer Betreuer] Schmidt, and Claudio [Akademischer Betreuer] Brunini. "Ionosphere modeling from GPS radio occultations and complementary data based on B-splines / Marco Limberger. Betreuer: Urs Hugentobler. Gutachter: Urs Hugentobler ; Michael Schmidt ; Claudio Brunini." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1077867409/34.
Повний текст джерелаYapici, Tolga. "Influences Of Interplanetary Magnetic Field On The Variability Of Aerospace Media." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608784/index.pdf.
Повний текст джерелаVanderburgh, Richard N. "One-Dimensional Kinetic Particle-In-Cell Simulations of Various Plasma Distributions." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1610313011646245.
Повний текст джерелаGurel, Ilker. "Channel Estimation For Ofdm Systems." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606940/index.pdf.
Повний текст джерелаFoucault, Etienne. "IONO-HF : propagation des ondes hautes fréquences dans l'ionosphère." Thesis, Toulouse 3, 2020. http://www.theses.fr/2020TOU30039.
Повний текст джерелаRadio wave propagation in high and very high frequency bands is a major subject of interest; mainly because of the rise of telecommunication and GPS technologies. Although, the effective transmission of these signals highly depends on the medium. There is a part of the neutral atmosphere, named ionosphere and located approximately between 60 and 2,000 km, which impact the wave propagation as it is composed of a partially ionised plasma. It is formed through the photo-ionization of neutral species by the solar UV and EUV spectrum. During my Ph.D., my first achievement was to develop a ray tracing tool to solve the HF and VHF radio wave trajectories in a realistic ionosphere. It is based on numerical development of the Fermat's Principle which allows trajectory modelling. To give more insight information on wave propagation, this tool also integrates some wave parameters such as propagation time, total electron content TEC and absorption. A simple tilted dipole magnetic field is implemented, which allow the ordinary and extraordinary propagation mode modelling. As a first application, I used this ray tracing tool to model a SuperDARN coherent HF radar. These radars are dedicated to the observation and study of the high latitude plasma convection. First, I studied the radio wave propagation in synthetic ionosphere profiles, featuring different types of electron density gradients. I have shown that ionosphere profile with a developed E region implies low altitude refraction for waves with low elevation angles and moderate to high absorption. For ionosphere profile with lower density E region, wave may propagate to higher altitude and form echoes region spanning across the F region, while being less absorbed. While adding horizontal electron density gradient in these ionosphere profiles, I have shown that the echoes region keep the same pattern but are shifted in distance respect to the radar. Then, I used these results to study the wave propagation in a realistic ionosphere featuring complex electron density gradients. As a second application, I studied the magnetic field effect on radio wave propagation by modelling the ordinary and extraordinary propagation modes in the case of a ionosonde. It is an instrument dedicated to the sounding of the local vertical electron density profile below the F region peak. In the case of a parallel propagation with respect to the magnetic field, the ray tracing tool modelled the expected behaviour for both propagation modes, in terms of different altitude of reflection and different propagation speed. While modelling ordinary and extraordinary modes in the case of a SuperDARN radar, I have shown that the magnetic field effect was negligible as the propagation is almost perpendicular respect to the magnetic field. [...]
Oliveira, Junior Paulo Sergio de. "Definition and implementation of a new service for precise GNSS positioning." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152111.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
PPP (Precise Point Positioning) is a positioning method by GNSS (Global Navigation Satellite Systems), based on SSR (State Space Representation) concept that can provide centimeter accuracy solutions. Real-time PPP (RT-PPP) is possible thanks to the availability of precise products, for orbits and clocks, provided by the International GNSS Service (IGS), as well as by its analysis centers such as CNES (Center National d'Etudes Spatiales). One of the remaining challenges on RT-PPP is the mitigation of atmospheric effects (troposphere and ionosphere) on GNSS signals. Thanks to recent improvements in atmospheric models, RT-PPP can be enhanced, allowing accuracy and centimeter initialization time, comparable to the current NRTK (Network Real-Time Kinematic) method. Such performance depends on topology of permanent stations networks and atmospheric conditions. The main objective of this project is to study the RT-PPP and the optimized infrastructure in terms of costs and benefits to realize the method using atmospheric corrections. Therefore, different configurations of a dense and regular GNSS network existing in France, the Orpheon network, are used. This network has about 160 sites and is owned by Geodata-Diffusion (Hexagon Geosystems). The work was divided into two main stages. Initially, ‘float PPP-RTK’ was evaluated, it corresponds to RT-PPP with improvements resulting from network corrections, although with ambiguities kept float. Further on, network corrections are applied to improve “PPP-RTK” where ambiguities are fixed to their integer values. For the float PPP-RTK, a modified version of the RTKLib 2.4.3 (beta) package is used to take into account for the network corrections. First-order ionospheric effects were eliminated by the iono-free combination and zenith tropospheric delay estimated. The corrections were applied by introducing a priori constrained tropospheric parameters. Periods with different tropospheric conditions were chosen to carry out the study. Adaptive modeling based on OFCs (Optimal Fitting Coefficients) has been developed to describe the behavior of the troposphere, using estimates of tropospheric delays for Orpheon stations. This solution allows one-way communication between the server and the user. The quality of tropospheric corrections is evaluated by comparison to external tropospheric products. The gains achieved in convergence time to 10 centimeters accuracy were statistically quantified. Network topology was assessed by reducing the number of reference stations (up to 75%) using a sparse Orpheon network configuration to perform tropospheric modeling. This did not degrade the tropospheric corrections and similar performances were obtained on the user side. In the second step, PPP-RTK is realized using the PPP-Wizard 1.3 software and CNES real-time products for orbits, clocks and phase biases of satellites. RT-IPPP (Real-Time Integer PPP) is performed with estimation of tropospheric and ionospheric delays. Ionospheric and tropospheric corrections are introduced as a priori parameters constrained to the PPP-RTK of the user. To generate ionospheric corrections, it was implemented a solution aligned with RTCM (Real-Time Maritime Services) conventions, regarding the transmission of ionospheric parameters SSR, which is a standard Inverse Distance Weighting (IDW) algorithm. The choice of the periods for this experiment was made mainly with respect to the ionospheric activity. The comparison of the atmospheric corrections with the external products and the evaluation of different network topologies (dense and sparse) were also carried out in this stage. Statistically, the standard RT-IPPP takes ~ 25 min to achieve a 10 cm horizontal accuracy, which is significantly improved by our method: 46% (convergence in 14 min) with dense network corrections and 24% (convergence in 19 min) with the sparse network. Nevertheless, vertical positioning sees its convergence time slightly increased, especially when corrections are used from a sparse network solution. However, improvements in horizontal positioning due to external SSR corrections from a (dense or sparse) network are promising and may be useful for applications that depend primarily on horizontal positioning.
O PPP (Precise Point Positioning) é um método de posicionamento pelo GNSS (Global Navigation Satellite Systems), baseado no conceito SSR (State Space Representation) o qual pode fornecer soluções de acurácia centimétrica. O PPP em tempo real (RT-PPP) é possível graças à disponibilidade de produtos precisos, para órbitas e relógios, fornecidos pelo IGS (International GNSS Service), bem como por seus centros de análise, como o CNES (Centre National d’Etudes Spatiales). Um dos desafios restantes no RT-PPP é a mitigação dos efeitos atmosféricos (troposfera e ionosfera) nos sinais GNSS. Graças às melhorias recentes nos modelos atmosféricos, o RT-PPP pode ser aprimorado, permitindo tempo de inicialização com acurácia centimétrica, comparável ao atual método NRTK (Network Real-Time Kinematic). Esse desempenho depende da topologia das redes de estações permanentes e das condições atmosféricas. O objetivo principal deste projeto é estudar o RT-PPP e a infraestrutura optimizada em termos de custos e benefícios para realizar o método usando correções atmosféricas. Portanto, são utilizadas diferentes configurações de uma rede GNSS densa e regular existente na França, a rede Orphéon. Esta rede tem cerca de 160 estações, sendo propriedade da Geodata-Diffusion (Hexagon Geosystems). O trabalho foi dividido em duas etapas principais. Inicialmente, foi avaliado o "float PPP-RTK", que corresponde ao RT-PPP com melhorias resultantes de correções de rede, embora mantendo as ambiguidades como float. Em um segundo momento, as correções de rede são aplicadas para aprimorar o "PPP-RTK", onde ambiguidades são fixadas para seus valores inteiros. Para o float PPP-RTK, uma versão modificada do software RTKLib 2.4.3 (beta) é empregada de modo a levar em consideração as correções de rede. Os efeitos ionosféricos de primeira ordem são eliminados pela combinação iono-free e atraso zenital troposférico é estimado. As correções são aplicadas introduzindo parâmetros troposféricos a priori injuncionados. Períodos com diferentes condições troposféricas foram escolhidos para realizar o estudo. Uma modelagem adaptativa baseada em OFCs (Optimal Fitting Coefficients) foi implementada para descrever o comportamento da troposfera, utilizando estimativas de atraso troposférico para estações da rede Orphéon. Tal solução permite a comunicação unidirecional entre o servidor e o usuário. A qualidade das correções troposféricas foi avaliada através de comparação com produtos externos troposféricos. Os ganhos alcançados no tempo de convergência para acurácia de 10 centímetros foram quantificados estatisticamente. A topologia de rede foi avaliada reduzindo o número de estações de referência (em até 75%) usando uma configuração da rede Orphéon esparsa para realizar a modelagem troposférica. Isso não degradou as correções troposféricas e foram obtidas performances similares para os usuários simulados. Na segunda etapa, o PPP-RTK é realizado usando o software PPP-Wizard 1.3, bem como os produtos para tempo real do CNES de órbitas, relógios e biases de fase dos satélites. O RT-IPPP (Real-Time Integer PPP) é realizado com estimativa de atrasos troposféricos e ionosféricos. As correções ionosféricas e troposféricas são introduzidas como parâmetros a priori injuncionados no PPP-RTK do usuário. Para gerar correções ionosféricas, foi implementada uma solução alinhada com as convenções RTCM (Real-Time Maritime Services), em relação à transmissão de correções ionosféricas SSR, o qual é um algoritmo baseado na ponderação pelo inverso da distância (IDW – Inverse Distance Weighting). A escolha dos períodos para este experimento foi realizada principalmente em relação à atividade ionosférica. A comparação das correções atmosféricas com produtos externos, assim como a avaliação de diferentes topologias de rede (densa e esparsa) também foram realizadas nesta etapa. Estatisticamente, o RT-IPPP padrão leva ~ 25 min para alcançar uma acurácia horizontal de 10 cm, a qual é significativamente melhorada pelo método implementado: 46% (convergência em 14 min) com correções de rede densa e 24% (convergência em 19 min) com a rede esparsa. No entanto, o posicionamento vertical vê o seu tempo de convergência ligeiramente aumentado, especialmente quando as correções são usadas a partir de uma solução de rede esparsa. No entanto, as melhorias no posicionamento horizontal com o uso das correções de SSR externas de uma rede (densa ou esparsa) são promissoras e podem ser úteis para aplicações que dependem principalmente do posicionamento horizontal.
Le PPP (Precise Point Positioning) est une méthode de positionnement par GNSS (Global Navigation Satellite Systems), basée sur le concept SSR (State Space Representation), qui peut générer solutions de précision centimétrique. Le PPP en temps réel (RT-PPP) est possible grâce à la disponibilité des produits précis, pour les orbites et horloges, fournis par l’IGS (International GNSS Service), ainsi que par ses centres d'analyse, tels que le CNES (Centre National d'Etudes Spatiales). Un des défis restants sur le RT-PPP est la mitigation des effets atmosphériques (troposphère et ionosphère) sur les signaux GNSS. Grâce aux améliorations récentes des modèles atmosphériques, le RT-PPP peut être amélioré, ce qui permet une précision et un temps d'initialisation au niveau du centimètre, comparables à la méthode NRTK (Network Real-Time Kinematic) actuelle. De telles performances dépendent de la topologie du réseau de stations GNSS permanentes et des conditions atmosphériques. L'objectif principal de ce projet est d'étudier le RT-PPP et l'infrastructure optimisée en termes de coûts et d'avantages pour réaliser la méthode en utilisant des corrections atmosphériques. Pour cela, différentes configurations d'un réseau GNSS dense et régulier existant en France, le réseau Orphéon, sont utilisées. Ce réseau compte environ 160 sites, propriété de Geodata-Diffusion (Hexagon Geosystems). Le travail est divisé en deux étapes principales. Dans un premier temps, le mode «PPP-RTK flottant» a été évalué, il correspond au RT-PPP avec des améliorations issues des corrections de réseau, mais avec les ambiguïtés flottantes. Ensuite, des corrections de réseau sont appliquées pour améliorer le mode « PPP-RTK » où les ambiguïtés sont fixées à leurs valeurs entières. Pour le PPP-RTK flottant, une version modifiée du package RTKLib 2.4.3 (beta) est utilisée pour prendre en compte les corrections réseau. Les effets ionosphériques de premier ordre ont été éliminés par la combinaison iono-free et le retard troposphérique zénithal est estimé. Les corrections ont été appliquées en introduisant des paramètres troposphériques a priori contraints. Des périodes avec différentes conditions troposphériques ont été choisies pour réaliser l'étude. Une modélisation adaptative basée sur les OFCs (Optimal Fitting Coefficients) a été mise en place pour décrire le comportement de la troposphère, en utilisant des estimations des retards troposphériques pour les stations Orphéon. Cette solution permet une communication mono-directionnelle entre le serveur et l'utilisateur. La qualité des corrections troposphériques est évaluée par comparaison avec des produits troposphériques externes. Les gains réalisés sur le temps de convergence pour obtenir un positionnement de 10 centimètres de précision ont été quantifiés statistiquement. La topologie du réseau a été évaluée, en réduisant le nombre de stations de référence (jusqu'à 75%), via une configuration de réseau Orphéon lâche pour effectuer la modélisation troposphérique. Cela n'a pas dégradé les corrections troposphériques et des performances similaires ont été obtenues du côté de l'utilisateur. Dans la deuxième étape, le PPP-RTK est réalisé grâce au logiciel PPP-Wizard 1.3 et avec les produits temps réel CNES pour les orbites, les horloges et les biais de phase des satellites. Le RT-IPPP (Real-Time Integer PPP) est réalisé avec estimation des délais troposphériques et ionosphériques. Les corrections ionosphériques et troposphériques sont introduites en tant que paramètres a priori contraints au PPP-RTK de l'utilisateur. Pour générer des corrections ionosphériques, il a été mis en place une solution alignée avec les conventions RTCM (Real-Time Maritime Services) pour la transmission des paramètres ionosphériques SSR, un algorithme standard d'interpolation à distance inversée (IDW – Inverse Distance Weighting). Le choix des périodes pour cette expérience a été fait principalement en regard de l'activité ionosphérique. La comparaison des corrections atmosphériques avec les produits externes et l'évaluation de différentes topologies de réseau (dense et lâche) ont également été effectuées dans cette étape. Statistiquement le RT-IPPP standard prend ~25 min pour atteindre une précision horizontale de 10 cm, ce que nous améliorons significativement par notre méthode : 46% (convergence en 14 min) avec le réseau dense et 24% (convergence en 19 min) avec le réseau restreint. Néanmoins le positionnement vertical voit son temps de convergence légèrement augmenté, en particulier lorsque l'on utilise des corrections à partir d'une solution de réseau lâche. Cependant, les améliorations apportées au positionnement horizontal dues aux corrections atmosphériques SSR externes provenant d’un réseau (dense ou lâche) sont prometteuses et peuvent être utiles pour les applications qui dépendent principalement du positionnement horizontal.
CNPq: 229828/2013-2
"Ionospheric Channel Modeling and Estimation." Master's thesis, 2017. http://hdl.handle.net/2286/R.I.46347.
Повний текст джерелаDissertation/Thesis
Masters Thesis Electrical Engineering 2017
"Three-dimensional, high resolution, computerized ionospheric tomographic imaging and computational modeling of an artificial ionospheric cavity." WEST VIRGINIA UNIVERSITY, 2008. http://pqdtopen.proquest.com/#viewpdf?dispub=3300883.
Повний текст джерелаChen, Yao-Chung, and 陳耀鐘. "A Novel Method For Regional Ionospheric VTEC Modeling and Computerized Ionospheric Tomography Using GPS Measurements: LS-MARS." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/93496958406955331650.
Повний текст джерела國立中興大學
土木工程學系所
102
At present, all proposed method for ionospheric vertical total electron content (VTEC) and electron density (ED) modeling using GNSS could be classified into two different categories: function-based and pixel-based. The key point of function-based method is to select an appropriate mathematical function for the distribution of ionospheric VTEC or ionospheric ED over modeling region thus effectively estimates the differential code bias of the receiver (RDCB), the differential code bias of the satellite (SDCB), VTEC or ED. However, the ionosphere not only varies periodically with the time and space, but also has short-term irregular disturbances because of solar activity and geomagnetic variations. The same function model is therefore unlikely to fit different ionospheric behaviors. And it has always bothered researchers for the selection of mathematical function with appropriate degree and order over modeling region. In order to solve these problems, this study proposed a novel function-based approach called LS-MARS. The LS-MARS uses Multivariate Adaptive Regression Splines (MARS) from the field of statistical learning to estimate the VTEC or ED approximate model first and then substitutes this model in the observation equation to form the normal equation. The Least Squares Method (LSM) is used to solve the unknown parameters. Compared with the conventional function-based method, the advantage of LS-MARS is that the optimal approximate model can be found automatically, precisely, flexibly and adaptively from the observations using MARS without a priori knowledge of the ionospheric VTEC or ED distribution mathematical function. The LS-MARS can simply construct VTEC (2D, 3D) and ED (3D, 4D) for different dimensions, or higher dimensional ionospheric model since MARS can model high dimensional data. The LS-MARS can enhance the function-based method for modeling performance and convenience and help to further research on the ionosphere. In this paper, the performance and reliability of the regional two-dimensional VTEC and three-dimensional ED modeled by using LS-MARS were studied. The results showed that the LS-MARS has good modeling effectiveness and reliability for modeling regional ionospheric VTEC and ED. Therefore, this method can serve as an attractive and alternative method for researchers in the field of ionosphere.
Tzeng, Duen-Bin, and 曾惇彬. "Modeling Ionospheric Effects with Multiple Reference Stations for GPS Satellite Surveying." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/69479068407984456206.
Повний текст джерела國立中央大學
土木工程研究所
89
Satellite surveying with the Global Positioning System (GPS) has shown several advantages over standard surveying techniques. However, because of some unmodeled systematic errors, the possibility of successful ambiguity resolution is poor in the processing of long baseline vectors. Therefore, the methods of modeling ionospheric errors and increasing measurement equations are proposed with multiple reference stations. There are two proposed method of estimating ionospheric delays; one is linear interpolation according to the positions of reference and rover stations, another is the least squares method considering a slant function. On the other hand, a network with several reference points can provide several known positions to form more baselines to rovers, so more degrees of freedom are available by increasing measurement equations of baselines. These baselines would be processed in a matrix system. Finally, for verification, three experiments were carried out. The results show that the proposal concept is helpful to ambiguity resolution and GPS surveying both with L1 frequency and dual-frequency data. The purpose of this thesis is to evaluate the help of multiple reference stations for GPS surveying.